The invention relates to a method for installing a converter bottom, in particular one provided with nozzles for introducing media, and in which the largest area on a bottom plate is lined with bottom bricks of commercial brick formats.
In the case of vessels for receiving molten metal, in particular molten iron, in the bottom of which vessels nozzles are provided for introducing various media into the molten metal, there is known to be a higher degree of wear of the refractory bottom bricks in comparison with the lining of the vessel. For this reason, bottom blowing steel making converters or iron bath reactors for producing gas and corresponding converters for melt reduction, for example, are provided with replaceable vessel bottoms. Such a treatment vessel, generally termed a "converter" here, has a dismountable bottom plate on which the bottom lining is located. The introduction nozzles are built into this refractory bottom lining, and the bottom is replaced by a new one when required, usually when the refractory material is worn down to the safety layer. The space which is left free during the installation of the bottom, i.e. the adjusting joint between the bottom walling and the vessel walling, is filled up with a refractory mass. When the entire converter is relined, this mass is rammed in, and when the bottom is changed in the heated vessel, the joint is filled in with a casting mass. In particular tar- or pitch-bound products on a magnesite and/or dolomite base have proved useful as refractory material for this purpose.
Under favorable operating conditions, at least one change of bottom is necessary during the converter campaign in the case of a steel making converter operated only with bottom nozzles or a combined blowing technique. In a first approximation, wear rates therefore result for the bottom lining which are about twice as high as for the side walling.
The absolute wear of the refractory material, for example in a steel making converter, depends on the operating conditions, in particular on the maximum temperature, usually the tapping temperature of the molten steel. Wear rates of 0.3 to 0.6 mm per charge come about for the vessel lining at an average tapping temperature of 1600.degree. C. in the case of the pitch-bound, low-iron magnesite bricks preferably used today, whereas a wear rate of approx. 1.6 mm per charge occurs at an average tapping temperature of 1680.degree. C. The wear of the bottom bricks is higher by a factor of 2, as already mentioned.
When the stress on the vessel linings increases, i.e. with increasing operating temperatures of the converter, there is further a superproportional degree of wear of the adjusting joint between the vessel bottom and the wall lining, which is lined with ramming or casting mass. Repairs are necessary to counteract premature wear in this area. For this purpose the preliminary worn joint is cast with a pitch-bound mass, as during the change of bottom in the hot vessel. Like the change of bottom itself, these repair measures, along with the subsequent heating and sintering of the casting mass, have a detrimental effect on the availability of the converter. Furthermore, the wear of the joint has an unfavorable effect on the durability of the bottom since the bricks at the edge of the bottom are rounded toward the joint and wear out more quickly than the center of the bottom.
In the past there has been no shortage of attempts to improve the durability of the bottom. Thus, a German Offenlegungsschrift No. 28 43 735 describes a bottom in which only one nozzle is arranged per row of bricks. Further, wider joints up to 2.5% of the maximum brick width are recommended in the bottom walling. However, no success has been achieved with the bottoms according to the teachings of this application. in reducing the wear rates of the bottom bricks to the magnitude of the converter lining in which these bottoms are installed.
German Pat. No. 26 54 232 relates to a method and an apparatus for producing nozzle bottoms for oxygen blowing converters with protection gas tuyeres, in which the channels for the nozzles are drilled after the bottom plate has been lined with the bricks. This method allows for older, partly warped bottom plates with dense joints to be lined with the bottom bricks without regard to shaped bricks for the nozzles. However, the bottoms produced according to this method do not eliminate the problem of the premature wear of the adjusting joint between the bottom walling and the converter lining, since the changeable bottoms can on principle only be installed when the converter lining is finished.